Dame's Rocket (Hesperis matronalis) on left 4/26/11 VA and right 5/27/06 Presque Isle, Erie, PA

Mustard family; white, purple, pink; toothed, opposite leaves; flowers with 4 petals.
http://www.ppws.vt.edu/scott/weed_id/hevma.htm
Up to 4 to 5 feet tall.
Leaves lanceolate.
Lower leaves larger and taper into short petiole.
Leaves get progressively smaller up the stem.
Leaves up top have no or short petioles.
Upper leaves hairy.
Silique (seedpod) 2-4" long.

Dame's Rocket:
http://plants.usda.gov/java/profile?symbol=HEMA3&photoID=hema3_001_avd.tif

see also:
http://www.ontarioweeds.com/weed.php?w=HEVMA